Wet etch process and composition for forming openings in a polymer substrate

ABSTRACT

A composition and method for etching a polymer substrate in particular for forming micro vias includes a dihydric alcohol having from two to five carbon atoms, a hydroxide compound selected from the group of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide and mixtures thereof, and water. In one embodiment the composition includes glycol, potassium hydroxide and deionized water, wherein the glycol and the water are present in a ratio of from about 0.5:1 to about 8.5:1 and the potassium hydroxide is present in an amount of from about 40 to about 80 grams per 100 ml of glycol and water solution.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. ProvisionalApplication No. 60/222,362, filed Aug. 1, 2000, the disclosure of whichis hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates in general to the field ofmicroelectronic elements, and more particularly, to chemical processesand compositions therefore for forming openings such as windows, viasand/or through holes in polymer substrates. Still more particularly, thepresent invention relates to etch compositions providing a color signalindicator at the completion of the etch process.

[0003] Windows, vias and other openings are common features incorporatedin microelectronic elements enabling the interconnection ofmicroelectronic components and circuit features on opposing sides of asubstrate, typically, a dielectric substrate such as a flexible sheet ofpolyimide. Micro-vias, i.e., those having a diameter of less than about100 microns, play an important role in high I/O density IC packages.There are known a number of techniques for making vias and/or otheropenings in polymer substrates. These techniques include laser ablation,photo imaging/plasma etching and chemical etching, of which chemicaletching has generally been preferred. In this regard, laser ablationoften leaves a residue which requires a subsequent plasma cleaning stepto remove the residue to enable the subsequent metalization process tobe performed. This two-step laser ablation process is not only timeconsuming, but also increases manufacturing costs. In addition, laserablation generally can only process one substrate at a time.

[0004] Chemical etching, on the other hand, has a number of advantageswhich cannot be obtained by laser ablation. For example, substrates canbe processed by either rack or batch processing for high productionrates. Chemical etching has been found to provide clean and even vias,providing a low cost and simple process with inherent workability. Inthis regard, chemical etching is suitable not only as an alternativeprocess for forming vias, but also for reworking of vias formed by laserablation and/or plasma etching techniques which have been incompletelyformed.

[0005] There are known various etching solutions suitable for formingvias and/or openings in flexible dielectric substrates such aspolyimide. For a variety of reasons, these known etching solutionssuffer a number of disadvantages wherein improvements in chemicaletching techniques have been sought. For example, alcohol-basedetchants, such as ethanol or isopropanol solutions as disclosed in U.S.Pat. No. 4,986,880 are highly volatile and evaporate quickly, i.e.,boiling point of about 160° F. These alcohol-based etchants are hard tocontrol due to rapid depletion of the active components.

[0006] Aqueous etching solutions such as known from U.S. Pat. Nos.5,350,487, 4,911,786, 4,857,143 and 4,353,778 are effective in removingthe polyimide material, but often cause contact pad blisters when usedin forming vias in two metal polyimide structures, i.e., a polyimidesubstrate clad on its opposing surfaces with a copper layer, or whenused with one metal polyimide structures. Another problem with usingaqueous etching solutions in single metal polyimide structures is that amask, a resist or another protect layer must be used to protect thesurface of the polyimide which is not metal clad.

[0007] Solvent-based etchants, such as TMAH-based as known from U.S.Pat. Nos. 4,369,090, 4,039,371, 5,597,983 and 5,653,893,hydrazinehydrate-based such as known from U.S. Pat. No. 4,436,583 and JP3101228A2, and hydroxylamine-based such as known from U.S. Pat. No.5,279,771 are known to attack adhesives that are commonly employed inframing processes used to stabilize the polyimide substrate such asdisclosed in U.S. patent application Ser. No. 09/134,212 entitled“Dicing in Registration With Solder Balls”, filed on Aug. 14, 1998 andassigned to the same assignee of the present application. Solvent-basedetchants are therefore undesirable due to the tendency to separate thecopper clad polyimide material from the glass frame. In addition, thesesolvent-based etchants will have the tendency to cause the coppercontact pads to form blisters by delamination of the contact pads fromthe polyimide substrate.

[0008] Accordingly, it can be appreciated that there is the need forfurther improvements in chemical etchants which avoid the abovedisadvantages, while being low cost, incorporating simple processtechniques and providing for reworkability of vias and openings formedby other techniques such as laser ablation and/or plasma etch processes.Still further, there is the desirability of providing a chemical etchantwhich provides a color indicator which signals completion of the etchingprocess. This ensures complete etching of the polymer substrate therebyminimizing operator error and the degree of reworking required informing vias and other openings.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention there is provided achemical etch composition for forming openings in polymer substrates, inparticular, micro-vias having a diameter of about 100 microns or less.The etchant compositions of the present invention further provide acolor indicator which signals completion of the etching process, e.g.,the appearance of a red color at the base of the opening being etched.

[0010] The present invention discloses glycol-based etchant compositionsfor etching openings, in particular, micro-vias, in polymer substrates.These etchant compositions have higher boiling points, by way ofexample, of preferably about 240° F. to 300° F., more preferably ofabout 260° F. to 280° F., and hence, are not highly volatile. Theetchant compositions of the present invention are more stable thanalcohol-based formulations, making them easier to control. In addition,glycol-based etchant compositions are less likely to attack the adhesivethat are typically used in microelectronic elements and/or in bondingmetal clad polyimide material to a glass frame. The method and etchantcompositions of the present invention produce clean and even vias oropenings in a two-step process, i.e., (1) dipping the substrate in theetchant composition, preferably until a red signal color covers the viaopening and (2) rinsing with pressurized water, i.e., about 30 psi,until the red color when present disappears from the via.

[0011] In accordance with one embodiment of the present invention thereis described a composition for etching a polymer substrate comprising adihydric alcohol having from two to five carbon atoms, a hydroxidecompound selected from the group consisting of lithium hydroxide, sodiumhydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide,strontium hydroxide and mixtures thereof, and water.

[0012] In accordance with one embodiment of the present invention thereis described a composition for etching a polymer substrate comprisingglycol, potassium hydroxide and deionized water, wherein the glycol andthe water are present in a ratio of from about 0.5:1 to about 8.5:1 andthe potassium hydroxide is present in an amount of from about 40 toabout 80 grams per 100 ml of glycol and water solution.

[0013] In accordance with one embodiment of the present invention thereis described a method for etching a polymer substrate to form a via, themethod comprising exposing a portion of the substrate to an etchantcomposition comprising a dihydric alcohol having from two to five carbonatoms, a hydroxide compound selected from the group consisting oflithium hydroxide, sodium hydroxide, potassium hydroxide, calciumhydroxide, barium hydroxide, strontium hydroxide and mixtures thereof,and water.

[0014] In accordance with one embodiment of the present invention thereis described a method for etching a via in a polyimide substratecomprising exposing a portion of the substrate to an etchant compositionat a temperature in the range of from about 170° to about 230° F., thecomposition comprising glycol, potassium hydroxide and deionized water,wherein the glycol and the water are present in a ratio of from about0.5:1 to about 8.5:1 and the potassium hydroxide is present in an amountof from about 40 to about 80 grams per 100 ml of glycol and watersolution, and continuing the exposing step until a portion of thecomposition covering the via changes color.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above description, as well as further objects, features andadvantages of the present invention will be more fully understood withreference to the following detailed description of a wet etch processand composition for forming openings in a polymer substrate, when takenin conjunction with the accompanying drawings, wherein:

[0016] FIGS. 1-3 are sequential diagrammatic illustrations of a processfor etching an opening such as a micro-via in a flexible polymersubstrate using an etchant composition in accordance with one embodimentof the present invention;

[0017]FIG. 4 is a diagrammatic illustration showing a metal cladflexible dielectric substrate having a via formed in accordance with thepresent invention which is used as a tented stencil for printing amaterial, such as flux or solder paste, onto the top surface of a solderball; and

[0018]FIG. 5 is a perspective diagrammatic illustration of a tentedstencil made in accordance with the present invention.

DETAILED DESCRIPTION

[0019] In describing the preferred embodiments of the present invention,specific terminology will be resorted to for the sake of clarity.However, the invention is not intended to be limited to the specificterms so selected, and is to be understood that each specific termincludes all technical equivalence which operate in a similar manner toaccomplish a similar purpose.

[0020] In accordance with the present invention, there is disclosed achemical etching process and chemical etchant composition for wetchemical etching of polymer substrates, e.g., polyimide, to formopenings such as bond windows, vias and other holes, and particularly,micro-vias, i.e., an opening having a diameter of about 100 microns orless, for interconnecting layers in flexible circuit structures ofmicroelectronic elements. The etching process and etchant compositionsare broadly based upon the presence of at least one dihydric alcohol anda strong base such as one or more hydroxide compounds.

[0021] Dihydric alcohols contemplated for use in accordance with thepresent invention include diols and glycols having a chain length ofpreferably 2 to 5 carbon atoms, and more preferably from 2 to 4 carbonatoms. In accordance with the preferred embodiment, the etchantcomposition includes ethylene glycol. Although it is contemplated thatdihydric alcohols having a chain length of 5 carbons or greater can beused, it is known that higher molecular weight diols and glycols willresult in increased viscosity to the etchant composition, therebyimparting poor wetting properties. In addition, as the molecular weightof the dihydric alcohol increases, it is contemplated that there may besolubility limitations of the other components, e.g., the hydroxidecompound, to form the required composition in the nature of a solutionwithout precipitation of the hydroxide compound.

[0022] Various strong bases such as hydroxide compounds are suitable foruse in the etchant composition in accordance with the present invention.For example, suitable hydroxide compounds include lithium hydroxide,sodium hydroxide, potassium hydroxide, calcium hydroxide, strontiumhydroxide, barium hydroxide and mixtures thereof. Using weaker hydroxidecompounds, although suitable, will result in longer etching times. Onthe other hand, stronger hydroxide compounds will result in shorteretching times. Although sodium hydroxide can be used, it may have thetendency to cause blisters at the contact pads, as well as being lesssoluble than other hydroxide compounds such as potassium hydroxidepotentially causing precipitation. When etching polyimide substrates,lithium hydroxide, barium hydroxide, strontium hydroxide, sodiumhydroxide and potassium hydroxide are preferred. Sodium hydroxide andpotassium hydroxide are most preferred. It is further contemplated thatmixtures of various hydroxide compounds can also be used, for example,potassium hydroxide, sodium hydroxide and others.

[0023] Broadly by way of example, the etchant compositions in accordancewith the present invention include from about 30 to about 100 ml ofdihydric alcohol, from about 15 to about 80 grams of a strong hydroxidebase, from about 1 to about 20 grams of an optional etch speedinhibitor, and up to about 70 mls of water, preferably deionized water.In the preferred etch composition of the present invention, the dihydricalcohol is a glycol, e.g., ethylene glycol, present from about 50 toabout 100 ml, the hydroxide base is potassium hydroxide from about 40 toabout 80 grams, from about 1 to 20 grams of etch inhibitor and fromabout 15 to 50 mls of deionized water. The etch speed inhibitor can beselected from compounds including NaF, CH₃COONa, CH₃COOK, K₂CO₃, Na₂CO₃,K₃PO₄ and hexamethylene tetramine, as well as mixtures thereof. The etchspeed inhibitor allows for additional control of the etch speed duringthe etching process.

[0024] The etchant compositions are generally prepared by combining thedihydric alcohol and deionized water in a vessel and adding a sufficientquantity of hydroxide base which would form a saturated solution atabout 150° F. A quantity of the etch speed inhibitor may optionally beadded. As the amount of water increases, the amount of hydroxide baseshould also be increased to maintain a saturated solution at theselected temperature. If water is lost during the process, or if thetemperature during the etching process drops, the hydroxide willgenerally not precipitate out. In this regard, it is contemplated thatthe etching process will occur at a temperature higher than thesaturation temperature of the etchant composition.

[0025] It has been determined that low concentrations of the base suchas potassium hydroxide may not produce the color signal at the end ofthe etching process. Therefore, it is preferred that higherconcentrations of hydroxide base be present in the etch compositionswhere a color signal is desired. The minimum amount of hydroxide basecan be determined experimentally, and preferably, should form at least a50% solution with the water present in the composition. The mechanism ofthe formation of a red color signal will be explained by way ofcontemplated theory, and is not to be interpreted as a limitation on thescope of the present invention. During the etching process, a hydrolysisreaction takes place in which the polyimide is broken down. The reactionproducts of this hydrolysis reaction can be referred to as ahydrolyzate. It is contemplated that one of the hydrolyzates has astructure which is similar to the structure of a phenolphthalein.Phenolphthalein is an acid-base indicator used in titration. When usingphenolphthalein, a pink color is observed when the pH is 8 and a redcolor is observed when the pH is about 10. It is contemplated that asthe hydrolysis reaction proceeds, a color indicating hydrolyzate isproduced but it is not until the etching is complete that concentrationof color-indicating hydrolyzate is sufficient to produce an obviouslyvisible red color, and hence, a color signal.

[0026] In accordance with a specific example, an etchant composition isprepared including from about 50 to about 100 ml ethylene glycol, fromabout 50 to about 40 grams potassium hydroxide, up to about 5 gramspotassium carbonate, and up to about 50 mls deionized water. The etchantcomposition is prepared as previously described for use in etching apolyimide substrate to form micro-vias having openings less than about100 microns in diameter.

[0027] A test substrate was prepared for etching. As shown in FIG. 1,the substrate 100 includes a polyimide flexible layer 102 and outermetal layers 104, 106. The polyimide layer 102 has a thickness ofapproximately 50 microns, while the metal layers 104, 106 each have athickness of about 5 microns. Generally, the metal layers are copperformed in a cladding or other depositing process. However, other metalsand composites such as nickel/chrome, tin/gold/chromium and the like canbe used in place of, or in addition to, copper.

[0028] One or both of the metal layers 104, 106 can be pre-etched into adesired pattern at the desired via sites to expose the polyimide layer102 in a predetermined pattern. In the case of single metal substratesfor use in making certain types of chip scale and near chip scalepackages, such as for example the assemblies disclosed in certainembodiments of commonly assigned U.S. Pat. Nos. 5,148,265 and 5,148,266,the disclosures of which are incorporated herein by reference, both bondwindow sites and via sites are exposed. In the case of two metalsubstrates for use in making certain other types of chip scale packageassemblies, such as for example assemblies disclosed in certainembodiments of commonly assigned U.S. Pat. No. 5,518,964, the disclosureof which is incorporated herein by reference, gold or gold/copper/goldtraces and leads 108 are plated on the metal layers 104, 106 on oppositesides of the substrate 100. The photoresist used in patterning thetraces and leads 108 is then stripped away using known techniques.

[0029] The resulting structure is shown in FIG. 2. The substrate 100 isdipped into the etchant composition at a temperature in the range offrom about 170° to about 23° F. for about 6 to 10 minutes and preferablyat a temperature of about 180° F. to about 210° F. During the etch time,the etchant composition will etch the polyimide layer until the metallayer 106 is exposed as shown in FIG. 3 forming vias 110. The etchantcompositions of the present invention indicate completion of the etchingprocess of the polyimide layer by appearance of a red signal color,i.e., color indicator, at the base of the via, bond window or otheropening being etched. The etchant compositions accordingly function bothas an etchant and as an indicator. The substrate is spray rinsed untilthe red color disappears completing the etching of the polyimide layer100.

[0030] Various etchant compositions were formulated in accordance withthe general formula of from about 50 to about 100 ml ethylene glycol,from about 40 to about 80 grams potassium hydroxide, from about 1 toabout 20 grams of etch speed inhibitor, and from about 15 to about 50mls of deionized water. Various etchant compositions were prepared forevaluation as follows: (a) water-based compositions containing deionizedwater and potassium hydroxide, (b) glycol-based compositions containingethylene glycol and potassium hydroxide, (c) etchant compositionscontaining varying amounts of deionized water, ethylene glycol andpotassium hydroxide, (d) etchant compositions containing deionizedwater, ethylene glycol, potassium hydroxide and different etchinhibitors, and (e) specific identified compositions.

[0031] Copper clad/polyimide test substrates 100, as previouslydescribed, were soaked in hot deionized water at a temperature of fromabout 140 to about 180° F. for 2 to 3 minutes. The purpose of thesoaking was to wet the polyimide and to drive bubbles out of thepatterned via areas. The substrates 100 were dipped in the etchantcompositions at 200° F. followed by post cleaning in hot water at atemperature of from about 140° to about 180° F. The cleaned substrates100 were spray rinsed with deionized water and dried with an air gun.The specific etchant compositions and observations are shown in thefollowing tables. FORMULA OBSERVATION a. Water base: Test 1: DI water100 ml; 200° F. boiling, pad peel off KOH 30 g Test 2: DI water 100 ml;200° F. 3 min.: discolor; KOH 60 g 5 min.: pad blister Test 3: DI water100 ml; 200° F. 5 min.: discolor; KOH 60 g; NaCO3 5 g 8 min.: padblister Test 4: DI water 100 ml; 200° F. 2 min.: red color; KOH 100 g 5min.: pad blister b. Glycol base: Test 5: Glycol 100 ml; 220° to 230° F.15 min. KOH 20g undercut Test 6: Glycol 100 ml; Hard to be dissolved KOH40 g c. Ration of water: Glycol Test 7: DI water 100 ml; 200° F. for 10minutes, 100% Glycol 20 ml; KOH of pad blister 60 g Test 8: DI water 100ml; 200° F. for 10 minutes, Glycol 50 ml; KOH about 50% blister 60 gTest 9: DI water 100 ml; 200° F. for 10 minutes, Glycol 50 ml; KOH about20% blister 80 g Test 10: DI water 50 ml; 200° F. for 10 minutes, Glycol50 ml; KOH blister 60 g Test 11: DI water 50 ml; 200° F. for 10 minutes,none Glycol 50 ml; KOH blister 80 g Test 12: DI water 50 ml; 200° F. for10 minutes, none Glycol 100 ml; KOH blister 60 g Test 13: DI water 30ml; 200° F. for 10 minutes, none Glycol 70 ml; KOH blister 60 g Test 14:DI water 20 ml; 200° F. for 10 minutes, none Glycol 80 ml; KOH blister50 g Test 15: DI water 10 ml; 200° F. for 10 minutes, none Glycol 90 ml;KOH blister 40 g d. Different additive/inhibitor: Test 16: DI water 100ml; 200° F. for 10 minutes, Glycol 50 ml; KOH blister 80 g; K2CO3 20 gTest 17: DI water 100 ml; 200° F. for 10 minutes, none Glycol 50 ml; KOHblister 80 g; K3PO4 20 g Test 18: DI water 100 ml; 200° F. for 10minutes, Glycol 50 ml; KOH blister 80 g; NaF 1.5 g Test 19: DI water 100ml; 200° F. for 10 minutes, none Glycol 50 ml; KOH blister 80 g;NaCH3COO 20 g Test 20: DI water 100 ml; 200° F. for 10 minutes, noneGlycol 50 ml; KOH blister 80 g; K3P04 10 g; Hexamethylene tetramine 0.5g e. Defined formula: 1. Glycol 100 ml; DI water 200° F. for 4 min., red50 ml; KOH 80 g; color; 6 min. discolor; 7 Hexamethylene tetramine min.finished, none blister 1 g 2. Glycol 100 ml; DI water 200° F. for 5min., red 50 ml; KOH 50 g; K3P04 20 g color; 7 min. finished, noneblister 3. Glycol 100 ml; DI water 200° F. for 3 min., red; 4 50 ml; KOH80 g; K3P04 min. discolor; 5 to 6 min. 1.5 g finished, none blister 4.Glycol 80 ml; DI water 200° F. for 4 min., red 20 ml; KOH 50 g; color; 8to 10 min. Hexamethylene tetramine finished, none blister 1 g 5. Glycol80 ml; DI water 200° F. for 6 min., red 20 ml; KOH 60 g; K3P04 5g color;8 to 10 min. finished, none blister 6. Glycol 85 ml; DI water 220° F.for 6 min., red 15 ml; KOH 40 ml color; 8 to 10 min. finished, noneblister 7. Glycol 50 ml; DI water 200° F. for 4 min., red 50 ml; KOH 75g; K3P04 10 g color; 6 to 7 min. finished, none blister 8. Glycol 50 ml;DI water 200° F. for 3 min., red 50 ml; KOH 80 g; color; 4 min.discolor; 5 Hexamethylene tetramine to 6 min. finished, none 1 g blister9. Glycol 50 ml; DI water 200° F. for 3 min., red 50 ml; KOH 80 g; K3P04color; 4 min. discolor; 5 1.5 g to 6 min. finished, none blister

[0032] The test data evidences that etching substrate 100 based on theuse of potassium hydroxide can effectively remove polyimide material informing vias. Of particular interest are forming micro-vias having adiameter of about 100 microns or less. In the formation of micro-vias,it is desirable that (1) any residual polyimide along the sidewalls becompletely removed, and (2) the copper layer, in particular the copperpads around the via openings should not be damaged by the etchant suchas by blistering or otherwise. To achieve these objectives, properetching speed and degree should be maintained during the etchingprocess. It is contemplated that proper etching speed and degree isdependent upon a number of factors, including the ratio of dihydricalcohol to water, the concentration of the hydroxide component, theinclusion of an etch speed inhibitor, processing temperature andprocessing time.

[0033] To avoid contact pad blistering based upon ethyleneglycol/potassium hydroxide compositions, it is contemplated that theratio of glycol to water should be in the range of from about 0.5:1 toabout 8.5:1. It has been observed that pad blistering occurs when theratio is less than about 0.5:1. The concentration of the hydroxidecomponent, in particular potassium hydroxide, is dependent upon theratio of glycol and water. By way of example, for 100 mls ofglycol/water solution, the range of potassium hydroxide should be fromabout 40 to about 80 grams. The more water, the more potassium hydroxideis required to provide an effective color signal at the completion ofthe etching process.

[0034] As previously noted, the addition of glycol to the etchantcomposition increases the boiling point thereby enabling higheroperating temperatures. It is contemplated that processing temperaturesin the range of from about 180° to about 230° F. will provide effectiveetching of the polyimide layer while minimizing pad blistering. If theprocess temperature is less than about 180° F., etching speed slowsthereby requiring longer processing times. In accordance with thepreferred embodiment, a processing temperature of about 180° to about210° F. is considered optimum. If the processing time becomes too long,significant undercutting of the contact pads around the via openings canoccur. It has been observed that if etching is completed in about 6 toabout 10 minutes, there is no evidence of pad blistering andundercutting is minimized. To assist in controlling of the etchingspeed, various inhibitors can be employed as previously described. Inaccordance with one embodiment, K₃PO₄ and hexamethylene tetramine arepreferred.

[0035] In accordance with another embodiment of the present invention, atwo metal flexible substrate, i.e., 5 microns copper/50 micronspolyimide/5 micron copper, was etched. The etchant composition was basedupon a formulation including ethylene glycol present in the range offrom about 50 to 100 ml, potassium hydroxide present in the range offrom about 40 to about 80 grams, deionized water present in the range offrom about 15 to about 50 ml, and hexamethylene tetramine in the rangeof from about 1 to 20 grams. The process of the present invention wascarried out using the latter etchant composition including the steps asfollows:

[0036] (1) Pre etch patterned copper foil at via sites to exposepolyimide (both window and via in the case of certain single metalsubstrates).

[0037] (2) Plate gold or gold-copper-gold traces and leads on oppositeside of the polyimide substrate (for two metal tape).

[0038] (3) Strip photoresist.

[0039] (4) Pretreatment: Dip substrate in hot DI water at about 160° F.to about 180° F. for 2 to 3 minutes.

[0040] (5) Dip substrate in the etching solution, at about 190° to about210° F. for 6 to 10 minutes, until red color covers the entire polyimidewindow.

[0041] (6) Post clean: Dip substrate in hot DI water at about 160° F. toabout 180° F. for 3 to 5 minutes, until red color disappears.

[0042] (7) Spray rinse: DI water spray at room temperature for 2minutes.

[0043] The etchant compositions of the present invention areparticularly unique in that in addition to being an etchant, they canindicate completion of the etching of the polyimide substrate byappearance of a red color at the base of the vias being etched. Chemicaletchant compositions based upon dihydric alcohols and strong hydroxidebases, and preferably glycols and potassium hydroxide, provide anetchant composition and process which can be used to form micro-vias forinterconnecting layers in microelectronic elements such as flexiblecircuit structures.

[0044] The etchant compositions of the present invention can be used forforming vias, bond windows and other openings in various microelectronicelements, such as two metal tape having plated through holes. By way ofexample, the etchant compositions of the present invention are suitablefor making microelectronic elements as disclosed in Application No.60/185,296 entitled “Single Image Process for Two-Sided Circuit” filedon Feb. 28, 2000, the disclosure of which is incorporated herein byreference.

[0045] Referring to FIGS. 4 and 5, the etchant compositions of thepresent invention can be used to manufacture a tented stencil 120 from ametal clad flexible sheet of polymer material, e.g., polyimide. Asshown, the etching process using the etchant compositions of the presentinvention, as thus far described, forms a through hole 112. The openingin metal layer 104 is larger than the opening in metal layer 106 as aresult of the etching process. The opening in metal layer 104 is largeenough to receive a solder ball 114 so as to partially extend into thevia. The opening in metal layer 106 can be used as a stencil mask forprinting a material, such as flux or solder paste, onto the top surfaceof the solder ball 114. Material 116 may be simultaneously stencilapplied to the top surfaces of a plurality of solder balls or solderbumps, by providing a stencil having a plurality of holes 112 which maybe arranged in a corresponding matrix pattern. Although the solder ballsor bumps may be attached to a common substrate or package during thestenciling operation, such attachment is not necessary. The plurality ofsolder balls may instead be free floating. The solder balls or bumps,such as C4 bumps, may be disposed on the face surface of a semiconductorchip during the stenciling operation. During the stenciling operation,the balls or bumps may instead be disposed on a surface of amicroelectronic element such as a semiconductor chip package, a waferpackage, a connection component, a substrate or the like such asgenerally designated by element 122. It should therefore be appreciatedthat the etchant compositions and process of the present invention canbe use for forming a variety of microelectronic elements.

[0046] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. Further, any range of numbers or ratios recited inthe specification or paragraphs hereinafter describing various aspectsof the invention, such as that representing a particular set ofproperties, units of measure, conditions, physical states orpercentages, is intended to literally incorporate expressly herein byreference or otherwise, any number falling within such range, includingany subset of numbers or ranges subsumed within any range so recited. Itis therefore to be understood that numerous modifications may be made tothe illustrative embodiments and that other arrangements may be devisedwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

1. A composition for etching a polymer substrate comprising a dihydricalcohol having from two to five carbon atoms, a hydroxide compoundselected from the group consisting of lithium hydroxide, sodiumhydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide,strontium hydroxide and mixtures thereof, and water.
 2. The compositionof claim 1, wherein said dihydric alcohol comprises glycol and saidhydroxide comprises potassium hydroxide.
 3. The composition of claim 1,further including an inhibitor selected from the group consisting ofNaF, CH₃COONa, CH₃COOK, K₂CO₃, Na₂CO₃, K₃PO₄, hexamethylene tetramine,and mixtures thereof.
 4. The composition of claim 1 wherein saiddihydric alcohol and said water are present in a ratio of from about0.5:1 to about 8.5:1.
 5. The composition of claim 4, wherein saidhydroxide compound is present in an amount of from about 40 to about 80grams per 100 ml of dihydric alcohol and water solution.
 6. Thecomposition of claim 1, wherein said hydroxide compound is present in anamount of from about 40 to about 80 grams per 100 ml of dihydric alcoholand water solution.
 7. The composition of claim 1, wherein said watercomprises deionized water.
 8. A composition for etching a polymersubstrate comprising glycol, potassium hydroxide and deionized water,wherein said glycol and said water are present in a ratio of from about0.5:1 to about 8.5:1 and said potassium hydroxide is present in anamount of from about 40 to about 80 grams per 100 ml of glycol and watersolution.
 9. The composition of claim 8, further including an inhibitorselected from the group consisting of NaF, CH₃COONa, CH₃COOK, K₂CO₃,Na₂CO₃K₃PO₄, hexamethylene tetramine, and mixtures thereof.
 10. A methodfor etching a-polymer substrate to form a via, said method comprisingexposing a portion of said substrate to an etchant compositioncomprising a dihydric alcohol having from two to five carbon atoms, ahydroxide compound selected from the group consisting of lithiumhydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide,barium hydroxide, strontium hydroxide and mixtures thereof, and water.11. The method of claim 10, wherein said dihydric alcohol comprisesglycol and said hydroxide comprises potassium hydroxide.
 12. The methodof claim 10, wherein said dihydric alcohol and said water are present ina ratio of from about 0.5:1 to about 8.5:1.
 13. The method of claim 12,wherein said hydroxide compound is present in an amount of from about 40to about 80 grams per 100 ml of dihydric alcohol and water solution. 14.The method of claim 10, wherein said hydroxide compound is present in anamount of from about 40 to about 80 grams per 100 ml of dihydric alcoholand water solution.
 15. The method of claim 10, wherein said watercomprises deionized water.
 16. The method of claim 10, wherein saidcomposition further includes an inhibitor selected from the groupconsisting of NaF, CH₃COONa, CH₃COOK, K₂CO₃, Na₂CO₃, K₃PO₄,hexamethylene tetramine, and mixtures thereof.
 17. The method of claim10, further including soaking said substrate before the exposing step inwater at a temperature of from about 160° to about 180° F.
 18. Themethod of claim 10, wherein said substrate is exposed to said etchantcomposition at a temperature of from about 170° to about 230° F.
 19. Themethod of claim 10, wherein said substrate is exposed to said etchcomposition at a temperature of from about 180° to about 210° F.
 20. Themethod of claim 10, further including cleaning said substrate after saidexposing step with water at a temperature in the range of from about160° to about 180° F.
 21. The method of claim 10, further includingexposing said substrate to said etchant composition until a portion ofsaid composition covering said via changes color.
 22. The method ofclaim 21, wherein said color comprises red.
 23. The method of claim 10,wherein said via has a diameter of about 100 microns or less.
 24. Themethod of claim 10, wherein said substrate comprises polyimide.
 25. Amethod for etching a via in a polyimide substrate comprising exposing aportion of said substrate to an etchant composition at a temperature inthe range of from about 170° to about 230° F., said compositioncomprising glycol, potassium hydroxide and deionized water, wherein saidglycol and said water are present in a ratio of from about 0.5:1 toabout 8.5:1 and said potassium hydroxide is present in an amount of fromabout 40 to about 80 grams per 100 ml of glycol and water solution, andcontinuing said exposing step until a portion of said compositioncovering said via changes color.
 26. The method of claim 25, whereinsaid temperature is in the range of from about 180° to about 210° F. 27.The method of claim 25, wherein said via has a diameter of about 100microns or less.
 28. The method of claim 25, wherein said colorcomprises red.
 29. The method of claim 25, further including cleaningsaid substrate after said exposing step with water at a temperature inthe range of from about 160° to about 180° F.
 30. The method of claim25, further including soaking said substrate before the exposing step inwater at a temperature of from about 160° to about 180° F.
 31. Thecomposition of claim 1, wherein said composition has a boiling point inthe range of from about 240° F. to about 300° F.
 32. The composition ofclaim 1, wherein said composition has a boiling point in the range offrom about 260° F. to about 280° F.
 33. The composition of claim 8,wherein said composition has a boiling point in the range of from about240° F. to about 300° F.
 34. The composition of claim 8, wherein saidcomposition has a boiling point in the range of from about 260° F. toabout 280° F.
 35. The composition of claim 1, wherein said substratecomprises a polyimide substrate.
 36. The composition of claim 8, whereinsaid substrate comprises a polyimide substrate.
 37. The method of claim10, wherein said composition has a boiling point in the range of fromabout 240° F. to about 300° F.
 38. The method of claim 10, wherein saidcomposition has a boiling point in the range of from about 260° F. toabout 280° F.
 39. The method of claim 25, wherein said composition has aboiling point in the range of from about 240° F. to about 300° F. 40.The method of claim 25, wherein said composition has a boiling point inthe range of from about 260° F. to about 280° F.
 41. A polymer substratehaving at least one via formed therein, said via formed by exposing aportion of said substrate to an etchant composition comprising adihydric alcohol having from two to five carbon atoms, a hydroxidecompound selected from the group consisting of lithium hydroxide, sodiumhydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide,strontium hydroxide and mixtures thereof, and water.
 42. The substrateof claim 41, further including a plurality of vias formed within saidsubstrate.
 43. The substrate of claim 42, wherein at least one of saidvias has a diameter of about 100 microns or less.
 44. The substrate ofclaim 41, wherein said substrate comprises a polyimide substrate. 45.The substrate of claim 41, wherein said substrate includes opposingfirst and second surfaces, and a first metal layer overlying said firstsurface, said first metal layer including an opening in alignment withsaid via.
 46. The substrate of claim 45, further including a secondmetal layer overlying said second surface, said second metal layerincluding an opening in alignment with said via.
 47. The substrate ofclaim 46, wherein the opening in said first metal layer is larger thanthe opening in said second metal layer.
 48. The substrate of claim 46,wherein said substrate includes a plurality of vias and a correspondingplurality of openings in said first and second metal layers.
 49. Thesubstrate of claim 41, wherein said dihydric alcohol and said water arepresent in a ratio of from about 0.5:1 to about 8.5:1.
 50. The substrateof claim 41, wherein said dihydric alcohol comprises glycol and saidhydroxide comprises potassium hydroxide.
 51. A polymer substrate havingat least one via formed therein, said via formed by exposing a portionof said substrate to an etchant composition at a temperature in therange of from about 170° to about 230° F., said composition comprisingglycol, potassium hydroxide and deionized water, wherein said glycol andsaid water are present in a ratio of from about 0.5:1 to about 8.5:1 andsaid potassium hydroxide is present in an amount of from about 40 toabout 80 grams per 100 ml of glycol and water solution, and continuingsaid exposing step until a portion of said composition covering said viachanges color.
 52. The substrate of claim 51, further including aplurality of vias formed within said substrate.
 53. The substrate ofclaim 52, wherein at least one of said vias has a diameter of about 100microns or less.
 54. The substrate of claim 51, wherein said substratecomprises a polyimide substrate.
 55. The substrate of claim 51, whereinsaid substrate includes opposing first and second surfaces, and a firstmetal layer overlying said first surface, said first metal layerincluding an opening in alignment with said via.
 56. The substrate ofclaim 55, further including a second metal layer overlying said secondsurface, said second metal layer including an opening in alignment withsaid via.
 57. The substrate of claim 56, wherein the opening in saidfirst metal layer is larger than the opening in said second metal layer.58. The substrate of claim 56, wherein said substrate includes aplurality of vias and a corresponding plurality of openings in saidfirst and second metal layers.
 59. The substrate of claim 51, whereinsaid dihydric alcohol and said water are present in a ratio of fromabout 0.5:1 to about 8.5:1.
 60. The substrate of claim 51, wherein saiddihydric alcohol comprises glycol and said hydroxide comprises potassiumhydroxide.
 61. A package comprising in combination a polymer substratein accordance with claim 41 and a microelectronic device having at leastone metal ball thereon received within said via.
 62. The package ofclaim 61, wherein said via has a diameter of about 100 microns or less.63. The package of claim 61, wherein said substrate includes opposingfirst and second surfaces, and a first metal layer overlying said firstsurface, said first metal layer including an opening in alignment withsaid via.
 64. The package of claim 63, further including a second metallayer overlying said second surface, said second metal layer includingan opening in alignment with said via.
 65. The package of claim 64,wherein the opening in said first metal layer is larger than the openingin said second metal layer.
 66. The package of claim 64, wherein saidsubstrate includes a plurality of vias and a corresponding plurality ofopenings in said first and second metal layers.
 67. A package comprisingin combination a polymer substrate in accordance with claim 51 and amicroelectronic device having at least one metal ball thereon receivedwithin said via.
 68. The package of claim 67, wherein said via has adiameter of about 100 microns or less.
 69. The package of claim 67,wherein said substrate includes opposing first and second surfaces, anda first metal layer overlying said first surface, said first metal layerincluding an opening in alignment with said via.
 70. The package ofclaim 69, further including a second metal layer overlying said secondsurface, said second metal layer including an opening in alignment withsaid via.
 71. The package of claim 70, wherein the opening in said firstmetal layer is larger than the opening in said second metal layer. 72.The package of claim 70, wherein said substrate includes a plurality ofvias and a corresponding plurality of openings in said first and secondmetal layers.